A tempest in a test tube is brewing in the case of Gigi Jordan, the pharmaceutical millionairess who admitted to fatally overdosing her 8-year-old son at The Peninsula hotel last year.

Jordan, 50, hopes to convince a jury that when she stuffed pills into both herself and her boy, Jude, she believed it was their only chance of escape from an alleged hell of sex abuse and death threats by the boy’s biological and adoptive fathers.

“We’re calling it an altruistic filicide defense,” Jordan’s lawyer, Ron Kuby, told The Post, adding that a big part of the case will be proving that the volume of drugs ingested by Jordan herself shows that she intended to die.

But only 1 milliliter of Jordan’s blood remains available for defense lawyers to use in proving this theory, Kuby notes in a letter to prosecutors.

That’s because prosecutors failed to order that Jordan’s blood be drawn in the hours after the semiconscious mother and the dead boy were carried out of the opulent hotel suite, Kuby complains.

The 1 milliliter — about one-fifth of a teaspoon — is all that is left from what Bellevue Hospital drew for testing while treating her.

Toxicology experts have advised the defense that 1 milliliter is too small a sample to confirm the levels of hydrocodone and benzodiazepine, the drugs Jordan says she ingested, Kuby argues.

Lead prosecutor Kerry O’Connell has suggested in court that Jordan was only faking suicide.